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b=/JqV+E+kA7M4Ue4qqa9B86A0fktCcKzRgjaOxs++GG4A+anB8+ANLEuppDVVUTVf7U37c5 6eCNnw4ZF47wYECw== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id DA4AF13721; Thu, 14 Nov 2024 08:23:58 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id AwCyNJ6zNWeEdQAAD6G6ig (envelope-from ); Thu, 14 Nov 2024 08:23:58 +0000 Message-ID: <1d9f9188-42b1-4f83-87e7-e02a22b67caa@suse.cz> Date: Thu, 14 Nov 2024 09:23:58 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 04/57] mm/page_alloc: Make page_frag_cache boot-time page size compatible Content-Language: en-US To: Ryan Roberts , Andrew Morton , Anshuman Khandual , Ard Biesheuvel , Catalin Marinas , David Hildenbrand , Greg Marsden , Ivan Ivanov , Kalesh Singh , Marc Zyngier , Mark Rutland , Matthias Brugger , Miroslav Benes , Will Deacon Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20241014105514.3206191-1-ryan.roberts@arm.com> <20241014105912.3207374-1-ryan.roberts@arm.com> <20241014105912.3207374-4-ryan.roberts@arm.com> From: Vlastimil Babka In-Reply-To: <20241014105912.3207374-4-ryan.roberts@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 4A93021992 X-Spam-Level: X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; FROM_HAS_DN(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[17]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.cz:+]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; ASN(0.00)[asn:25478, ipnet:::/0, country:RU]; RCVD_VIA_SMTP_AUTH(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns] X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Score: -4.51 X-Spam-Flag: NO On 10/14/24 12:58, Ryan Roberts wrote: > "struct page_frag_cache" has some optimizations that depend on page > size. Let's refactor it a bit so that those optimizations can be > determined at run-time for the case where page size is a boot-time > parameter. For compile-time page size, the compiler should dead code > strip and the result is very similar to before. > > One wrinkle is that we don't know if we need the size member until > runtime. So remove the ifdeffery and always define offset as u32 (needed > if PAGE_SIZE is >= 64K) and size as u16 (only used when PAGE_SIZE <= > 32K). We move the members around a bit so that the overall size of the > struct remains the same; 24 bytes for 64-bit and 16 bytes on 32 bit. > > Signed-off-by: Ryan Roberts Looks ok, but ideally the PAGE_FRAG_CACHE_MAX_ORDER #define should also be replaced by some variable that's populated just once. It can be static local to page_alloc.c as nothing else seems to use it. > > page_alloc > --- > > ***NOTE*** > Any confused maintainers may want to read the cover note here for context: > https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/ > > include/linux/mm_types.h | 13 ++++++------- > mm/page_alloc.c | 31 ++++++++++++++++++------------- > 2 files changed, 24 insertions(+), 20 deletions(-) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 4854249792545..0844ed7cfaa53 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -544,16 +544,15 @@ static inline void *folio_get_private(struct folio *folio) > > struct page_frag_cache { > void * va; > -#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) > - __u16 offset; > - __u16 size; > -#else > - __u32 offset; > -#endif > /* we maintain a pagecount bias, so that we dont dirty cache line > * containing page->_refcount every time we allocate a fragment. > */ > - unsigned int pagecnt_bias; > + unsigned int pagecnt_bias; > + __u32 offset; > + /* size only used when PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE, in which > + * case PAGE_FRAG_CACHE_MAX_SIZE is 32K and 16 bits is sufficient. > + */ > + __u16 size; > bool pfmemalloc; > }; > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 91ace8ca97e21..8678103b1b396 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4822,13 +4822,18 @@ static struct page *__page_frag_cache_refill(struct page_frag_cache *nc, > struct page *page = NULL; > gfp_t gfp = gfp_mask; > > -#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) > - gfp_mask = (gfp_mask & ~__GFP_DIRECT_RECLAIM) | __GFP_COMP | > - __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC; > - page = alloc_pages_node(NUMA_NO_NODE, gfp_mask, > - PAGE_FRAG_CACHE_MAX_ORDER); > - nc->size = page ? PAGE_FRAG_CACHE_MAX_SIZE : PAGE_SIZE; > -#endif > + if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) { > + gfp_mask = (gfp_mask & ~__GFP_DIRECT_RECLAIM) | __GFP_COMP | > + __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC; > + page = alloc_pages_node(NUMA_NO_NODE, gfp_mask, > + PAGE_FRAG_CACHE_MAX_ORDER); > + /* > + * Cast to silence warning due to 16-bit nc->size. Not real > + * because PAGE_SIZE only less than PAGE_FRAG_CACHE_MAX_SIZE > + * when PAGE_FRAG_CACHE_MAX_SIZE is 32K. > + */ > + nc->size = (__u16)(page ? PAGE_FRAG_CACHE_MAX_SIZE : PAGE_SIZE); > + } > if (unlikely(!page)) > page = alloc_pages_node(NUMA_NO_NODE, gfp, 0); > > @@ -4870,10 +4875,10 @@ void *__page_frag_alloc_align(struct page_frag_cache *nc, > if (!page) > return NULL; > > -#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) > /* if size can vary use size else just use PAGE_SIZE */ > - size = nc->size; > -#endif > + if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) > + size = nc->size; > + > /* Even if we own the page, we do not use atomic_set(). > * This would break get_page_unless_zero() users. > */ > @@ -4897,10 +4902,10 @@ void *__page_frag_alloc_align(struct page_frag_cache *nc, > goto refill; > } > > -#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) > /* if size can vary use size else just use PAGE_SIZE */ > - size = nc->size; > -#endif > + if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) > + size = nc->size; > + > /* OK, page count is 0, we can safely set it */ > set_page_count(page, PAGE_FRAG_CACHE_MAX_SIZE + 1); >